c - 当客户端将消息写入服务器时，但服务器无法在 linux 上的 c/c++ 中的 sokcet 中读取来自客户端的消息

Question

我的操作系统是 linux。我在C中编写套接字。我同时测试了客户端和服务器。它们都在我的本地主机上。但是，当客户端向服务器写消息时，服务器却无法从客户端读取消息。我不知道这是怎么回事。我确定客户端和服务器相互连接。我的主要目的是客户端将内容为序列号的消息写入服务器，然后服务器可以将消息回复给客户端。

我使用 pthread 使客户端可以连接到多个服务器。来自client.c的部分函数代码:

#include<stdio.h>
#include<string.h>    //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<netdb.h> //hostent
#include <pthread.h>
#include <ctype.h>
#include <stdint.h>
#include <limits.h>
#include <assert.h>
#include <sys/time.h>
#include <pthread.h>
#include <sys/select.h>
#include <unistd.h>
#include <fcntl.h>
#define NAMEMAX 4096
int socket_desc;
int packet_num;
struct timeval timeout;
typedef struct server_object{
    char server_ip[100];
    uint16_t server_port;
    struct sockaddr_in server_about;
}server_object; 

void* request(void* server_func){
    server_object* server_pointer = (server_object*) server_func;
    struct timeval start;
    struct timeval end;
    struct timeval thistimeout;
    int num = 0;
    //Connect to remote server
        int test_con = connect(socket_desc , (struct sockaddr *)&(server_pointer->server_about) , sizeof(server_pointer->server_about));
    printf("test_con = %d\n", test_con);    
    fd_set read_fd2;
    FD_ZERO(&read_fd2);
    FD_SET(socket_desc, &read_fd2);
    int fdmax2;
    fdmax2 = socket_desc;
    /*int ret2 = select(fdmax2+1, &read_fd2, NULL, NULL, &thistimeout);
    if(ret2 == 0){
        printf("00\n");
        printf("timeout when connect to %s:%u, seq = %d\n", server_pointer->server_ip, server_pointer->server_port, num);
        fflush(stdout);
        return 0;
    }*/
        //puts("Connected\n");
        //Send some data
    //while-loop begin
    int overtime = 0;
    while((num < packet_num && packet_num != 0) || (packet_num == 0)){
        char msg[200];
        memset(msg, 0, sizeof(msg));
        //strcpy(msg, "GET / HTTP/1.1\r\n\r\n");
        sprintf(msg, "%d", num);
        unsigned  long diff;
            gettimeofday(&start,NULL);
        printf("msg = %s\n", msg);
        ssize_t write_s;
        write_s = write(socket_desc, msg, sizeof(msg));
        printf("write_s = %ld\n", write_s);
        printf("msg = %s\n", msg);
            //puts("write failed");
        assert(num <= INT_MAX);
        //puts("Data Send\n");
        fd_set read_fd;
        FD_ZERO(&read_fd);
        FD_SET(socket_desc, &read_fd);
        int fdmax;
        fdmax = socket_desc;
        //int ret = select(fdmax+1, &read_fd, NULL, NULL, &thistimeout);    
        //if(ret == 0){
        //  overtime = 1;
        //  break;
        //}
        //Receive a reply from the server
        char buf[2000];
        printf("readbef\n");
        read(socket_desc, buf, sizeof(buf));
        printf("readafter\n");
        printf("buf = %s\n", buf);
        gettimeofday(&end,NULL);
        diff = 1000000 * (end.tv_sec-start.tv_sec)+ end.tv_usec-start.tv_usec;
        thistimeout.tv_usec -= diff;
        //printf("thedifference is %ldmsec\n",diff);
        //printf("buf = %s\n", buf);
            //puts("Reply received\n");
        printf("recv from %s:%u, seq = %d, RTT = %lu msec\n", server_pointer->server_ip, server_pointer->server_port, num, diff);
        fflush(stdout);
        num++;
    }
    if(overtime == 1){
        printf("timeout when connect to %s:%u, seq = %d\n", server_pointer->server_ip, server_pointer->server_port, num);
        fflush(stdout);
    }
    return 0;
}

int main(int argc , char *argv[]){
        sscanf(argv[1], "%d", &packet_num);
    //printf("packet_num = %d\n", packet_num);
    timeout.tv_sec = 0;
    sscanf(argv[2], "%lu", &timeout.tv_usec);
    //printf("timeout.tv_sec = %lu, timeout.tv_usec = %lu\n", timeout.tv_sec, timeout.tv_usec);
        //Create socket
        socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    printf("socket_desc = %d\n", socket_desc);
    int j = 3;
    int t;
    int isip = 1;
    while(j < argc){
        //int new_socket
        //struct sockaddr_in server;
        server_object server;
        char hostname[NAMEMAX] = {0};
        uint16_t portnum = 0;
        int meet = 0;
        int k;
        for(k = 0; k < strlen(argv[j]); k++){
            if(argv[j][k] == ':'){
                //portnum = argv[j]+(k+1);
                meet = 1;
                t = (k+1);
                continue;
            }
            if(meet == 0){
                hostname[k] = argv[j][k];
                if(isdigit(argv[j][k]) || argv[j][k] == '.'){
                    isip = 1;
                }
                else{
                    isip = 0;
                }
            }
            if(meet == 1){
                portnum = portnum*10 + (argv[j][k] - '0');
            }
        }
            char ip[100];
        memset(ip, 0, sizeof(ip));
            struct hostent *he;
            struct in_addr **addr_list;
            int i;
        struct in_addr hipaddr;
            if(isip){
            inet_aton(hostname, &hipaddr);
            he = gethostbyaddr(&hipaddr, 4, AF_INET);
        }
        else{
                he = gethostbyname( hostname );
        }
        //Cast the h_addr_list to in_addr , since h_addr_list also has the ip address in long format only
        addr_list = (struct in_addr **) he->h_addr_list;
            for(i = 0; addr_list[i] != NULL; i++){
                //Return the first one;
                strcpy(ip , inet_ntoa(*addr_list[i]) );
            }

            //printf("%s resolved to : %s\n" , hostname , ip);
        strcpy(server.server_ip, ip);
        //printf("port = %u\n", portnum);
        server.server_port = portnum;
            server.server_about.sin_addr.s_addr = inet_addr(ip);    
            server.server_about.sin_family = AF_INET;
            server.server_about.sin_port = htons(portnum);
        //thread start
        pthread_t ntid;
        pthread_create(&ntid, NULL, request, &server);
        sleep(10);
        j++;
        }
        return 0;
}

我使用 pthread 使服务器可以接受多个客户端。来自server.c的部分函数代码:

#include <stdio.h>
#include <string.h>    //strlen
#include <stdlib.h>    //strlen
#include <sys/socket.h>
#include <arpa/inet.h> //inet_addr
#include <unistd.h>    //write
#include <pthread.h> //for threading , link with lpthread
#include <netinet/in.h>
#include <sys/time.h>
int sv_socket_desc;
typedef struct client_object{
    struct sockaddr_in client_about;
    int client_fsd;
}client_object;

void *connection_handler(void *);

int main(int argc , char *argv[]){
    int new_socket , c;
    struct sockaddr_in server , client;     
    //Create socket
    sv_socket_desc = socket(AF_INET , SOCK_STREAM , 0); 
    printf("sv_socket_desc = %d\n", sv_socket_desc);
    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    //uint16_t portnum;
    //sscanf(argv[1], "%hu", &portnum);
    //server.sin_port = htons(portnum);
    server.sin_port = htons( 8888 ); 
    //Bind
    bind(sv_socket_desc,(struct sockaddr *)&server , sizeof(server));
    //Listen
    listen(sv_socket_desc , 3);     
    //Accept and incoming connection
    c = sizeof(struct sockaddr_in);
    while( (new_socket = accept(sv_socket_desc, (struct sockaddr *)&client, (socklen_t*)&c)) ){
        //puts("Connection accepted");         
        //Reply to the client
        client_object* new_sock;
        client_object newclient;
        newclient.client_about = client;
        newclient.client_fsd = new_socket;
        //start thread
        fflush(stdout);
        pthread_t sniffer_thread;
        new_sock = (client_object*)malloc(sizeof(client_object));
        *new_sock = newclient;
        fflush(stdout);
        pthread_create( &sniffer_thread , NULL ,  connection_handler , (void*) new_sock);
        sleep(10);
        //thread over
        //Now join the thread , so that we dont terminate before the thread
        pthread_join( sniffer_thread , NULL);
        //puts("Handler assigned");
    }     
    return 0;
}

/*
 * This will handle connection for each client
 * */
void *connection_handler(void *socket_desc){
    //Get the socket descriptor
    client_object newclient = *(client_object*) socket_desc;
    ssize_t read_size;
    char client_message[200];
    memset(client_message, 0, sizeof(client_message));
    unsigned short int client_port_num = ntohs(newclient.client_about.sin_port);
    char client_addr[2000];
    inet_ntop(AF_INET6, &(newclient.client_about.sin_addr.s_addr), client_addr, INET6_ADDRSTRLEN);
    /*fflush(stdout);
    read_size = read(sv_socket_desc, client_message, sizeof(client_message));
    printf("client_msg = %s\n", client_message);
    printf("read_size = %ld\n", read_size);
    fflush(stdout);*/
    while(1){
        //(read_size = read(sv_socket_desc, client_message, sizeof(client_message))) >= 0
        //printf("readbef\n");
        read_size = read(sv_socket_desc, client_message, sizeof(client_message));
        printf("read_size = %ld\n", read_size);     
        printf("client_message = %s\n", client_message);
        fflush(stdout);
        read_size = write(sv_socket_desc, client_message, sizeof(client_message));
        int n;
        sscanf(client_message, "%d", &n);
        printf("recv from %s:%hu, seq = %d\n", client_addr, client_port_num, n);
        fflush(stdout);
    }
    fflush(stdout);
    //Free the socket pointer
    free(socket_desc);
    return 0;
}

Answer 1

@Eddie Lin,你在 server.c 的 connection_handler() 中传递了错误的 fd。

请将 sv_socket_desc 替换为 newclient.client_fsd，因为接受返回 FD 用于通信目的，sv_socket_desc 是用于监听新连接的套接字。

while(1){
        //printf("readbef\n");
        read_size = read(newclient.client_fsd, client_message, sizeof(client_message));
        printf("read_size = %ld\n", read_size);
        printf("client_message = %s\n", client_message);
        fflush(stdout);
        read_size = write(newclient.client_fsd, client_message, sizeof(client_message));
        int n;
        sscanf(client_message, "%d", &n);
        printf("recv from %s:%hu, seq = %d\n", client_addr, client_port_num, n);
        fflush(stdout);
    }